/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import java.util.Iterator;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An ordering that uses the reverse of a given order.
 */
@GwtCompatible(serializable = true)
@ElementTypesAreNonnullByDefault
final class ReverseOrdering<T extends @Nullable Object> extends Ordering<T>
        implements Serializable
{
    final Ordering<? super T> forwardOrder;

    ReverseOrdering(Ordering<? super T> forwardOrder)
    {
        this.forwardOrder = checkNotNull(forwardOrder);
    }

    @Override
    public int compare(@ParametricNullness T a, @ParametricNullness T b)
    {
        return forwardOrder.compare(b, a);
    }

    @SuppressWarnings("unchecked") // how to explain?
    @Override
    public <S extends T> Ordering<S> reverse()
    {
        return (Ordering<S>) forwardOrder;
    }

    // Override the min/max methods to "hoist" delegation outside loops

    @Override
    public <E extends T> E min(@ParametricNullness E a, @ParametricNullness E b)
    {
        return forwardOrder.max(a, b);
    }

    @Override
    public <E extends T> E min(
            @ParametricNullness E a, @ParametricNullness E b, @ParametricNullness E c, E... rest)
    {
        return forwardOrder.max(a, b, c, rest);
    }

    @Override
    public <E extends T> E min(Iterator<E> iterator)
    {
        return forwardOrder.max(iterator);
    }

    @Override
    public <E extends T> E min(Iterable<E> iterable)
    {
        return forwardOrder.max(iterable);
    }

    @Override
    public <E extends T> E max(@ParametricNullness E a, @ParametricNullness E b)
    {
        return forwardOrder.min(a, b);
    }

    @Override
    public <E extends T> E max(
            @ParametricNullness E a, @ParametricNullness E b, @ParametricNullness E c, E... rest)
    {
        return forwardOrder.min(a, b, c, rest);
    }

    @Override
    public <E extends T> E max(Iterator<E> iterator)
    {
        return forwardOrder.min(iterator);
    }

    @Override
    public <E extends T> E max(Iterable<E> iterable)
    {
        return forwardOrder.min(iterable);
    }

    @Override
    public int hashCode()
    {
        return -forwardOrder.hashCode();
    }

    @Override
    public boolean equals(@CheckForNull Object object)
    {
        if (object == this)
        {
            return true;
        }
        if (object instanceof ReverseOrdering)
        {
            ReverseOrdering<?> that = (ReverseOrdering<?>) object;
            return this.forwardOrder.equals(that.forwardOrder);
        }
        return false;
    }

    @Override
    public String toString()
    {
        return forwardOrder + ".reverse()";
    }

    private static final long serialVersionUID = 0;
}
